Preparation Of 5-hydroxymethylfurfural From Cellulose With Porous Solid Acid Catalyst

Facing the dual pressures of environmental pollution and energy shortage, the development of new clean renewable energy is imperative. Biomass is considered to be a more ideal alternative energy source due to its advantages such as renewable nature, rich resources and low pollution. 5-hydroxymethylfurfural（HMF） is a platform compounds on the basis of biomass, is expected to be as a substitute precursor for non-renewable oil resources. The effective and low cost conversion of cellulose into HMF with porous solid acid catalyst is an important way in effectively utilize biomass energy, and the prospects is broad.Porous solid acid catalyst has become a hot spot in the research field of biomass energy because it has the advantages of easy separation, low corrosion of equipment, large specific surface area, low density, high porosity and low industrial wastewater. In this topic, three types of porous solid acid were synthesized according to the water-in-oil（W/O） Pickering high internal phase emulsions（HIPEs） templating, meanwhile, the conversion of one-pot cellulose to 5-hydroxymethylfurfural in the presence of 1-ethyl-3-methyl-imidazolium chloride（[Emim]Cl） was achieved by the porous solid acid. The main contents are summarized as follows:（1） Based on W/O Pickering HIPEs containing the oil phase of divinylbenzene（DVB）and water phase of saline solution, stabilized by both hydrophobic silica nanoparticles and Span 80, the porous polymer materials were prepared. After going through sulfonation in H₂SO₄ and hypercrosslinked process, the porous solid acids with large specific surface area were also synthesized. The catalysts exhibited mesopores within macropores stable structure,high BET specific surface area and more super-strong acid sites. Three variables of reaction conditions were optimized via response surface methodology, and the sequence of the three variables affecting HMF yield followed the order reaction temperature > reaction time >amount of catalyst, meanwhile, HMF yield of 29.2 % was obtained. Researches show that BET specific surface area and super-strong acid site both played key roles in cellulose conversion（2） Based on W/O Pickering HIPEs containing the oil phase of 1-octene, DVB and trihydroxymethylpropyl trimethylacrylate（TMPTMA） and water phase of saline solution,stabilized by both hydrophobic amino-functionalized nanoparticles and Span 80, the porous polymer materials were prepared. After going through sulfonation in H₂SO₄ process, a seriesof porous solid acid-base catalyst were also synthesized. Their properties with mesopores within macropores stable porous structure, acid-base strength and wettability could be controlled via changing the content of DVB, TMPTMA, 1-octene and nanoparticles.Moreover, the HMF yield was affected by these factors in the following order: surface hydrophobicity > acid-base bi-functionailty > acid strength > hierarchical porous structure >mesoporous structure, and HMF yield of 41 % was obtained. Researches show that hydrophobic surface, acid-base and porous structure played key roles in cellulose conversion.（3） Based on W/O Pickering HIPEs containing the oil phase of acidic prepolymers as analogous particles, DVB and styrene and water phase of saline solution, stabilized by both acidic prepolymers as analogous particles and Span 80, the porous polymer materials were prepared. After going through ion-exchange process with H⁺ and Cr³⁺, hydrophobic Br?nsted-Lewis double acid site porous solid acid were also synthesized. Lewis and Br?nsted acid sites were both fixed on the surface of cell of the catalysts, meanwhile,different optimal HMF yields（42.1 %, 64 %, 91 %） were achieved by one-pot conversion of cellulose, glucose and fructose to HMF with Cr³⁺-HPFs-1-H⁺and HPFs-1-H⁺, respectively.Researches show that Lewis acid sites had almost no influence on the HMF yield of fructose came from the function of Br?nsted acid sites; based on Lewis acid sites promote the reaction of glucose isomerization to fructose, Lewis acid sites were in favor for improving the HMF yield from cellulose and glucose.（4） The chemical and physical properties of three types of porous solid acids were characterized and ensured according to ¹³C CP/MAS NMR, FT-IR, XPS, TG-DSC,NH₃-TPD, CO₂-TPD, SEM, N₂ adsorption, EDS and Py-IR analyses, and three types of porous solid acids were very easily reused at least four times and the HMF yield was not significantly reduced.